For conventional high-voltage MOSFETs, the voltage blocking capability in the drain drift region is developed by having a thick epitaxial region and light doping. This results in most of the device ON resistance being in the drain drift region, which cannot be improved by known approaches used for low-voltage transistors (e.g., cell shrink, trench cells and smaller cell pitch), where only a small portion of the ON resistance is in the drain drift region.
Super junction MOSFETs are known which feature a unique drain structure. The main current path is through a more heavily doped (typically by a factor of 10) region than the doping in the main current path for a conventional high-voltage MOSFET. This lowers the ON resistance of the drain. There are also columns under the MOS cell doped opposite to the drain which provides a charge compensation structure that raises the breakdown voltage. For conventional NMOS super junction devices, there are p-columns under the cell structure, which can raise the breakdown voltage to about 600V from would otherwise be about 100V. The current path of the p-column and n-doped structures are dimensioned so that when the transistor is turning OFF and developing the blocking voltage, the resulting depletion region forms with migration of the charge carriers from the p-doped columns, resulting in a near-neutral space charge region and as a result higher blocking-voltage capability.